Wow. Noteplan looks great. It is a true Mac app and has a companion iOS app, allows files to be stored locally, supports Markdown, hides URL details for a cleaner look, collapses and expands detail under headings. What’s not to like?
Byword, TaskPaper, Obsidian, Craft, and now Noteplan. They are each great in their own ways. I’d like to use them all. 
It is a very nice app but as I outlined above, there are several things I don’t like:
TaskPaper, Obsidian and NotePlan can in theory be used together with the same notes …
What could be the advantage, to do so?
Those apps seems to be pretty redundant.
They aren’t necessarily redundant because they are good at different things.
NotePlan and TaskPaper are great with tasks. NotePlan integrates closely with your calendar and can time-block tasks in the calendar view. Obsidian can display Mermaid charts beautifully.
So say you have a note that includes tasks that you want to lay out in a calendar view, others that you don’t, and also a diagram.
You could use the same plain-text note for all three.
That’s a contrived example, but I do often use a couple different apps with the same note, depending what I’m doing with the note at any given time.
Tried latest version and still don’t like it. Prefer Things & Agenda. High annual subscription $ is a turn off too.
I see a lot to like in Noteplan.
I think if you want to create a digital bullet journal, it’s absolutely perfect for that. I like the calendar integration. I like the clarity of the UI. If I were lookng for a digital bullet journal, or an alternative for daily journaling, I’d use this. If you use Reminders, or want to start using them, this is a really useful app.
But as much as I like a lot about Noteplan, I’m going to keep using an analog bullet journal.
But I don’t have the bandwidth to make good use of them all. I’m going to have to make a decision. 
Good luck!
Two quick thoughts:
Like any toolset, your work can probably adapt as long as you have most of what you need.
And if you wind up settling on one of the tools that uses a folder of plain markdown notes, your decision isn’t permanent. If you find you really need some feature the other one has, or one of them comes out with some great new feature, you can switch fairly easily.
I like the concept of a single folder of notes but the location apparently forced on developers for sandboxed apps is ugly in the extreme!
/Users/USERNAME/Library/Containers/co.noteplan.NotePlan3/Data/Library/Application Support/NotePlan
Yes. This is my biggest problem with NotePlan. Probably the only one I candy find my way around so far.
Couldn’t you just place the folder as a favorite in finder, to work with this folder like every other folder?
Sure, I’ve done that. It’s still ugly.
Create an alias with a different name?
Thanks, but not worth the effort at this point. All-in-one apps like NotePlan are appealing to me at first but then I find that I miss the smaller more tightly focused apps that I have stumbled on and used for months and years. So after standing in awe of Obsidian, Craft, and NotePlan, I’ll probably stick to what I’ve been doing with Byword, TaskPaper, EagleFiler, Due, and Itsycal.
That is pretty much where I landed as well, just with a different set of apps.
Kind of the Unix philosophy right? Small apps that do one thing and one thing well. 
Okay, I gotta know. Where did you land? Pretty sure DEVONthink was one but you’ll have to forgive me for not being able to keep up with all of your app explorations! 
Well, I’m happy to report that I’m not going to embarrass myself—for once! 
I have not changed much at all from where I’ve been for several months now. So, here is where I am:
DT: I’ve used DT for a long time-the real change is moving from indexing to importaing my research
Apple Stock Apps: Reminders, Notes, Calendar, iWork, Podcast, Messages, Photos
Drafts-free version
Ulysses for most writing
Word for my book project
Bookends for citations
PDF Expert
IThoughts
Logos Bible
And a few of what I consider utilities:
That pretty much it. I struggled for a long while trying to decide about other apps including iA Writer, Obsidian, Craft, Things 3, Noteplan (tried for two week trial), and Scrivener (finally abandoned for reasons I’ve noted previously).
As I review that list I realize that I really have achieved a minimalist approach and in doing so I’m able to get all of my work done with little app overhead and friction and at modest cost.
If you are using Ulysses for your writing, why are you using Word for your Book Project.
I thought that Ulysses was the one often recommended to/from authors?